INDUSTRIAL VENTILATION by

Dr. N.C. Srivastava

1.0 Objectives: Control of -

Heat and local discomforts Odours Hazardous contaminants (dust particles, toxic gases, smoke and fumes etc.)

to achieve - Better health and safety of workers Increase in work efficiency and production

2.0 Principles: 1. Heat and contaminants should be exhausted at source for better control. 2. Ventilation can be a natural draft or a mechanical system or a combination of both.

A mechanical supply and exhaust system provides best control. It includes - Inlet/outlet sections - filters, cooling and heating equipment in supply system - filters and contaminants eliminating devices in exhaust system - fan sections - supply/exhaust duct work - air distribution terminals

3. Care that neighbourhood (including all living beings, agricultural crop, buildings etc.) are not adversely affected by exhausted air.

3.0 Control Measures:

3.1. Heat Control hot-dry areas (heat load on the worker is sensible or radiant; rate of cooling by evaporation of sweat is not reduced) warm-moist areas (a wet process giv6s latent heat and increases moisture content results in serious reduction in heat loss by evaporation of swet; is more hazardous than hot-dry areas)

Heat stress: is the thermal condition of the environment that in combination with metabolic heat generation of the body causes deep bod)' temperature to exeed 38°C

WBGT (Wet bulb globe temperature) is recommended index for heat stress in hot environments (fig. I ) and is determined as follows:

Outdoors with solar load: WBGT = 0.7 t n w + 0.2 tg + 0.1 t d b

Indoors or outdoors without solar load:

where

WBGT = 0.71. nw 0.3 to

t m v = natural wetbulb temp. : td(, = dry bulb temperature t 3 = V e r r \ o n a l o b e

O s o m m «*'»«•)

3 2

3 0

iu 28 j-ui i CI t O 13 26 m

2 4

CONTINUOUS WORK 7 S \ WORK. 2S%.REST EACH HOUR 5 0 1 WORK. 50" . REST EACH HOUR

WORK. 7 5 \ REST EACH HOUR

— —i I 1 I 100 200

LIGHT WORK

HEAT EXPOSURE LIMIT, WATTS

300 400 500

MOOERATE WORK HEAVV WOOK

Fig. 1 Heat Stress by WBGT Method

- 2 -

3.2 Local discomfort parameters:

Air Speed: Discomfort from drafts or high air speeds may affect work efficiency and sprains in body parts. Table I gives recommended air speeds for general ventilation for various working conditions.

Radiant temperature: Heat radiations form hot roof or sunlit walls may cause discomfort in the work place and may call for radiation shielding specially in mdustnal sheds.

Temperature & Humidity: Control of temperature and humidity simultaneously is required in special industrial applications as indicated in table - 2» Thes* Gcwditar>s call for specially designed air-conditioning system including ventilation.

4.0 General Ventilation: A general ventilation system supplies and/or exhausts air to provide heat control, dilute

contaminants to acceptable limits and replace exhaust air. by either natural supply or mechanical supply and'or exhaust systems. In most cases, the objective is to provide tolerable working conditions rather than total comfort. General ventilation rates should be high enough to dilute the carbon dioxide produced by the occupants. Out door air may be unsatisfactory or may need pretreatment if it is known to have high unacceptable contaminants levels. Vent.latum rafes jor cecTairt Hos^taJ ar«<x£ a iegtuen foi le-4 '

4.1 Natural ventiattion: Natural ventilation is a controlled flow of air caused by thermal and wind pressures and is effective

in work areas with significant heat release, as shown in fig. 0. . It is not suitable if pretreatment of the supply air is required.

4.2 Spot cooling: Convective spot cooling is an effective and efficient way of acceptable working conditions in the

work areas of a large factory building. Workers are exposed to air with increased velocities and desired temperature as indicated in table 3

4.3 Air distribution Location: for low level ventilation, the outlets should be at about 3m. for spot coo ling the outlets

should be close to worker at about 2m level. Some air supply design strategies are shown in fig J & L\

AIR OUTLET

Fig. 2. Natural Ventilation of Single Bay Building

Table 1 Acceptable Air Speed in Workplace

Activity I-evel Air Speed, m'/s

Cont inuous exposure Air-conditioned space Fixed workstation, general ventilation or spot cooling

Silting Standing

Intermittent exposure, spot cooling or relief stations Light heat loads and activity Moderate heat loads and activity High heal loads and activity

0.25 to 0.4

0 4 10 0.6 0 5 io 1.0

5 io 10 10 to 15 15 ty 20

a. Air is supplied by nonattached horizontally projected jet, b. Air is supplied by horizontally projected jet attached to the ceiling, and occupied zone is ventilated by reverse flow. and occupied zone is ventilated by reverse flow.

OCCUPIED ZONE

c. Air is supplied by horizontally projected concentrated air jets and vertical and/or horizontal directing jets, and occupied zone is ventilated by reverse flow and vertical directing jets.

Fig. 3 Concentrated Air Supply Methods

With inclined cooled air jets b. With inclined heated air jets

c. With radial jets attached to the ceiling

d. With downward projected e With downward projected conical jets compact jets

OCCUPIED ZONE

f. Through the wall-mounted grille; occupied zone ventilated by the jet directly

g. Through the wall-mounted grille; occupied zone ventilated by jet and reverse flow

OCCUPIED ZONE

— V OCCUPIED ZONE

Fig. 4 Nonconcentrated Air Supply Methods

- 4 -

T a b l e d Temperatures and Humidities for Industrial Air Conditioning Process Dry Bulb (°C) rh ( » )

ABRASIVE

Manufacture 26 50

C E R A M I C S

Refractorv 43 to 66 5 0 to 9 0 Molding room 27 6 0 to 7 0 Clay storage 16 to 27 35 to 65 Decalcomama production 24 to 27 48 Decorating room 24 to 27 48

Use high-efficiency filtration in decorating room. To minimize the danger of silicosis in other areas, a dust-collecting system or medium-eff ic iency paniculate air filtration may be required.

D I S T I L L I N G

General manufacturing 16 to 24 45 to 60 Aging 18 to 22 50 io 60

Low humidity and dust control are important w'here grains are ground. Use high-efficiency filtration for all areas to prevent mold spore and bacteria growth Use ultrahigh efficiency filtration where bulk f h s h pasteurization is performed.

E L E C T R I C A L P R O D U C T S

Electronics and X-ray Coil and transformer winding 22 15 Semiconductor assembly 20 40 to 50

Electrical instruments

Manufacture and laboratory 21 50 to 55 Thermostat assembly and calibration 24 50 to 55 Humidistat assembly and calibration 24 50 to 55

Small mechanisms

Close tolerance assembly 22* 40 to 45 Meter assembly and test 24 60 to 63

Switchgear

Fuse and cutout assembly 23 50 Capacitor winding 23 50 Paper storage 23 50

Conductor wrapping with yam 24 65 to 70 Lightning arrester assembly 20 20 to 40 Thermal circuit breakers assembly and test 24 30 to 60 High-voltage transformer repair 26 5 Water w heel generators

Thrust runner lapping 21 30 to 50

Rectifiers

Processing selenium and copper oxide plates 23 30 to 40 •Temperature to be held constant

Dust control is essential in these processes Minimum control requires medium-efficiency filters Degree of filtration depends on the type of func-tion in the area. Smaller tolerances and miniature components suggest high-efficiency particulate air filters.

F L O O R C O V E R I N G

Linoleum

Mechanical oxidizing of linseed oil* 32 to 38 Printing 27 Stoving process 70 to 120

• P r e c i s tempera ture control required

Medium-efficiency particulate air filtration is recommended for the siev-ing process

Process Dry Bulb <°C> r h ( % )

FOUNDRIES*

Core making 16 to 21

Mold making

Bench woik 16 to 21

Floor work 13 to 18

Pouring 4

Shakeout 4 to 10

Cleaning room 13 io 18

•Winter dressing room temperatures. Spot coolers are sometimes used in larger installations.

In mold making, provide exhaust hoods at t r a n t e r points v.ith wet-collector dust removal system Use280 to 380 L/s per hood.

in shakeout room, provide exhausi hoods with wet-collector dust removal system. Exhaust l90 to 240 L/s in grate area. Room ventilatory are generally not effective.

In cleaning room, provide exhaust hoods for grinders and cleaning equip-ment with dry cyclones or bag-type collectors. In core making, oven and adjacent cooling areas require fume exhaust hoods Pouring rooms require two-speed powered roof ventilators. Design for minimum of lO L/s per square metre of floor area at low speed. Shielding is required to control radi-ation from hot surfaces Proper introduction of air minimizes preheat requirements.

FUR

Drying

Shock treatment

Storage

43

- 8 to - 7

4 i o 10 55 to 65

Shock treatment or eradication of any insect infestations requires lower-ing the lemperature to -8 to - 7 ° C for 3 to 4 days, then raising it to 16 to 21°C for 2 days, then lowering it again for 2 days and raising it to the stor-age temperature

Furs remain pliable, oxidation is reduced, and color and luster are pre-served when stored at 4 to 10°C.

Humidity control is required to present mold growth (which is prevalent with humidities above SO^t) and hair splitting (uh ich is common with humidities lower than 55<H

G U M

Manufacturing 33

Rolling 20 63

Stripping 53

Breaking 23 47

Wrapping 23 58

L E A T H E R

Drying 20 to 52 75

Storage, winter room temperature 10 to 16 40 to 6 0

After leather is moistened in preparation for rolling and stretching, it is placed in an atmosphere held at room temperature with a relative humidity of 95%.

Leather is usually stored in warehouses without temperature and humidity control. However, it is necessary to keep humidity sufficiently low to prevent mildew. Medium-efficiency paniculate air filtration is recommended for fine finish.

L E N S E S ( O P T I C A L )

Fusing

Grinding

24

27

45

80

Table 3L Temperatures and Humidities for Industrial Air Conditioning (Concluded) Process Dry Bulb (°C) rh(S>) Process Dry Bulb (®C) rh

MATCHES Manufacture

Drying

Storage

22 to.23

21 to 24

16 to 17

50

60

50

Water evaporates with the sening of the glue. The amount of water evapo-rated is 8 to 9 kg per million matches The match machine turns out about 750,000 matches per hour

P A I N T A P P L I C A T I O N

Lacquers: Baking

Oils paints: Paint spraying

150 to 180

16 to 32 80

The required air filtration eff iciency depends on the painting process. On fine finishes, such as car bodies, high-efficiency particulate air filters are required for the outdoor air supply. Other products may require only low- or medium-efficiency filters.

Makeup air must be preheated. Spray booths must have 0.5 m/s face velocity if spraying is performed by humans: lower air quantities can be used if robots perform spraying. Ovens must have air exhausted to maintain fumes below explosive concentration Equipment must be explosion-proof. Exhaust must be cleaned by filtration and solvents reclaimed or scrubbed.

P H O T O S T U D I O

Dressing room 22 to 23 40 to 50 Studio (camera room) 22 to 23 4 0 to 5 0 Film darkroom 21 to 22 45 to 55 Print darkroom 21 to 22 45 to 55 Drying room 32 to 38 35 to 45 Finishing room 22 to 24 40 to 55 Storage room (b/w film and paper) 22 to 24 4 0 to 60 Storage room (color fi lm and paper) 4 to 10 4 0 to 5 0 Motion picture studio 22 4 0 to 55

The above data pertain to average conditions. In some color processes, elevated temperatures as high as 40°C are used, and a higher room tempera-ture is required.

Conversely, ideal storage condit ions for color materials necessitate refrig-erated or deep-freeze temperatures to ensure quality and color balance when long storage times are anticipated.

Heat liberated during printing, enlarging, and drying processes is removed through an independent exhaust system, which also serves the lamp houses and dryer hoods. All areas except finished film storage require a minimum of medium-eff ic iency particulate air filters.

P L A S T I C S

Manufacturing areas

Thermoset t ing molding compounds 27 25

Cellophane wrapping 24 to 27 45

In manufacturing areas where plastic is exposed in the liquid > molded, high-efficiencv particulate air filters may be required Dust uon and fume control are essential.

P L Y W O O D

Hot pressing (resin) 32

Cold pressing 32 15

R U B B E R - D I P P E D G O O D S

Manufacture 32

Cementing 27 25

Dipping surgical articles 24 to 27 25

Storage prior to manufacture 16 to 24 40

Laboratory (ASTM Standard) 23.0

"Dew point of air must be belov. evaporation temperature of solvent

Solvents used in manufacturing processes are often explosive an requiring positive ventilation. Volume manufacturers usually insial vent-recovery system for area exhaust systems

T E A

Packaging 18

Ideal moisture content is 5 to 69c for quality and mass. Low-lim ture content for quality is 4*3:.

T O B A C C O

Cigar and cigarette making 21 to 24 55

Softening 32 85

Stemming and stripping 24 to 29 7C

Packing and shipping 23 to 24

Filler tobacco casing and conditioning 24

Filter tobacco storage and preparation 25

Wrapper tobacco storage and conditioning 24

•Relative humidity fairly constant with range as set by cigarette machine.

Before stripping, tobacco undergoes a softening operation.

Table 3 Recommended Spot Cooling Air Speed and Temperature

Air Speed in J e t , Average Air T e m p e r a t u r e , °C, in Je t Cross Section

on 0.1 m : Heat Flux Density. W / m 2

Activity I^evel of Workp l ace 140-350 700 1400 2100 2KOO

Light—1 1 28 24 21 16 — Light—1 i — 28 26 24 20

3 — 28 26 24

3 5 — - — ~>7 25

Moderate—11 1 27 22 — — -

•> 28 24 21 16 —

3 — 27 24 21 18

3.5 — 28 25 22 19

Heavy—III 2 25 19 16 — — Heavy—III 3 26 n 20 IS r

3.5 — 23 n 20 19

—

Table •A General Pressure Relationships and Ventilation of Certain Hospital Areas Pressure Minimum Air Minimum Total All Air Air Recirculated

Relationship Io Changes of Out- AirChan&es Exhausted Directly YVithin Function Space Adjacent Areas door Air per Hour" per Hour" •o Outdoors Room Units S U R G E R Y A N D C R I T I C A L C A R E

Operat ing r o o m f a l l o u t d o o r air s y s t e m ) P I V 15 Yes N o (rec ircu lat ing air s y s t e m ) P s 2 5 O p t i o n a l N o

D e l i v e r y r o o m (all o u t d o o r air s y s t e m ) P 15 15 O p t i o n a l N o (rec ircu lat ing air s y s t e m ) 1' 5 2 5 O p t i o n a l N o

R e c o v e r y r o o m E 6 O p t i o n a l N o Nursery suite P s 12 O p t i o n a l N o Trauma room1 1 P 5 12 O p t i o n a l N o

A n e s t h e s i a storage ( s e e c o d e r e q u i r e m e n t s ) ± O p t i o n a l 8 Yes N o

N U R S I N G

Patient r o o m c i 2 4 O p t i o n a l O p t i o n a l Toi let r o o m ' N O p t i o n a l 10 Yes N o Intens ive care P 2 6 O p t i o n a l N o

O p t i o n a l " 1' iotect ive i so la t ion* P 15 Yes N o

O p t i o n a l "

In fec t i ous I s o l a t i o n 8 i 6 Yes N o Isolat ion a l c o v e or a n t e r o o m » -i 10 Yes N o 1 . a b o r / d e l i v e r y / r e c o v e r y / p o s t p a r t u m ( L D R P ) F. -i 4 O p t i o n a l O p t i o n a l Patient corridor-' E -i 4 O p t i o n a l O p t i o n a l

A N C I L L A R Y

R a d i o l o g \ X - r a y ( s u r g e r y and cri t ical c a r e ) P 3 15 O p t i o n a l N o

X-ray ( d i a g n o s t i c and t r e a t m e n t ) ± 2 6 O p t i o n a l O p t i o n a l

D a r k r o o m N •> 10 Yes' N o Laboratory, general N 2 6 Y e s N o Laboratory, b a c t e r i o l o g y N 2 6 Y e s N o Laboratory, b i o c h e m i s t r y P 2 6 O p t i o n a l N o 1 .uboratory. c y l o i o g y N 6 Yes N o

l a b o r a t o r y , g l a s s w a s h i n g N O p t i o n a l 10 Yes O p t i o n a l Laboratory, h i s to logy N i 6 Yet N o Laboratory, nuc lear m e d i c i n e N 2 6 Yes N o Laboratory , p a t h o l o g y N -> 6 Yes N o Laboratory, s e r o l o g y P -t 6 O p t i o n a l N o l a b o r a t o r y , s ter i l i z ing N O p t i o n a l 10 Yes N o L a b o r a t o r y m e d i a transfer P -i 4 O p t i o n a l N o A u t o p s y N 2 12 Yes N o Nonre fr igera ted b o d y - h o l d i n g r o o m ' N O p t i o n a l 10 Yes N o P h a r m a c y P -i 4 O p t i o n a l O p t i o n a l

A D M I N I S T R A T I O N

A d m i t t i n g a n d Wait ing R o o m s N 2 6 Yes O p t i o n a l

D I A G N O S T I C A N D T R E A T M E N T

B r o n c h o s c o p y , sputum c o l l e c t i o n , and p e n t a m i d i n e admin i s tra t ion N i 1 0 Yes Optional1"' E x a m i n a t i o n r o o m 0

* 2 6 O p t i o n a l O p t i o n a l M e d i c a t i o n r o o m P 4 O p t i o n a l O p t i o n a l Treatment r o o m ' ± •t - O p t i o n a l O p t i o n a l Phys i ca l therapy and h y d r o t h e r a p y N 2 6 O p t i o n a l O p t i o n a l S o i l e d w o r k r o o m o r s o i l e d h o l d i n g N > 10 Yes N o C l e a n w o r k r o o m o r c l e a n h o l d i n g " P 4 O p t i o n a l O p t i o n a l

S T E R I L I Z I N G A N D S U P P L Y

Ster i l i zer e q u i p m e n t r o o m N O p t i o n a l 10 Yes N o S o i l e d o r d e c o n t a m i n a t i o n r o o m N -i 6 Yes N o C l e a n w o r k r o o m and steri le s t o r a g e P 2 4 O p t i o n a l O p t i o n a l E q u i p m e n t s torage ± : i O p t i o n a l i -i O p t i o n a l O p t i o n a l

S E R V I C E

F o o d preparat ion c e n t e r s 1 * 2 10 Yes N o Warew a s h i n g N O p t i o n a l 10 Yes N o D i e t a r y day s t o r a g e ± O p t i o n a l O p t i o n a l N o Laundry, genera l N 10 Y e s N o S o i l e d l inen sort ing and s t o r a g e N O p t i o n a l 10 Yes N o C l e a n l inen s torage P 2 l O p u o n a l i ~> O p t i o n a l O p t i o n a l L i n e n and trash c h u t e room N . O p t i o n a l 1 0 Yes N o B e d p a n r o o m N O p t i o n a l 10 Y e s N o B a t h r o o m N O p t i o n a l 10 O p t i o n a l ' N o Jani tor ' s c l o s e t N O p t i o n a l 10 O p t i o n a l N o

P - P o s i t i v e N = N e g a t i v e ± = C o n t i n u o u s d irec t iona l contro l not required 0

•Ventilation in accordance wi th A S H R A E Siarulani 62 -1989 . Ventilation for Acceptable IikJoot Air Qualits. should be used for area* for which specific ventilaii«Hi rates arc not g n e n V> here a higher outdoor air requirement is called for in SianJard 62 than in Table 3 . the higher value should be used 'Total air changes indicated should be either supplied or. v.here required, exhaus ted T o r operating rooms. 100> outside air should dc used o n h w hen codes require it and o n h if heat recovery d e \ kcs are used <>Thc term trauma room as used here is the first aid r o o m and /o r emergencs room used for general initial treatment of accident victims. The operat ing r o o m within the t rauma center thai is rou l ineh used for emergeocs surgery should be treated as an operat ing room. Although cont inuous directionaJ control U not required, variation* >hould be minimized,

and in no case sh.njld a lack of directional control allow- the spread of infect ion f r o m one area lo another. Boundaries between funct ional areas (wards or ocpanment -0 should have d i n x -uonal control Lewi* (1988) descr ibes methods for mainta ining directional contro l b\ appi> -ing air tracking controls For a discussion of design considerat ions for central toilet exhaust sys tems, see the section

or. Patient Rooms

-The infect ious isolation room* .described in this table are those that might be used. !«>r infec-tious patients in the average community hospital The rooms are nega t i \eK prvssun /od Some isolation rooms ma\ have a separate an teroom. Refer to the d i sc i s s ion ir. chapter tor more detailed informat ion Where h i g h h infect ious respirable diseases such a- 'uberculosis arc to be isolated, increased air change rates should he considered.

Protect ive isolation rooms arc those used for immu.i t ' suppressed patient*. ITv room i* po-»i iivclv p r e s s u n / e d to protect the patient A n t e r o o m s art' generally required and should be nega-tivelv p r e s s u n / e d with respect to the patient room. R e c i r c u l a t i o n is a l lowed in r o o m s with possible respirators isolation patient*, if suppU air is HEPA t l l tea^j 'All air need not be exhaus ted il d a r k r o o m equipment has scavenging exhaust duct attached and meets ventilation s tandards o | N I O S H . O S H A . and local employee e x p o - w e limits JThe nt «tre frige rated bod) holding room exists o n h in facilities thai do not per torm autopsies on-site and use the space for short per iods whi le wait ing lor the KkIn to he transferred l F o o d preparat ion centers should have an excess of air s u p p h lor positive pressure * h c n hoods are not in operation The number of air changes mas be reduced or varied for odor con-trol when the space is not in use M i n i m u m total air changes per hour should he that required to provide proper makeup air to ki tchen exhaust sys tems. Sec O u p t e r 28 . Kitchen Ventilation.

4.4 Exhaust systems: Industrial exhaust systems should collect and remove air borne contaminants of particulates,

vapours and gases that can create an unsafe, unhealthy or undesired atmosphere both with in the space and outside surroundings.

Types of systems -General exhaust for entire work space without local considerations

Local exhaust: comprise of five components namely: hoods, duct system, air cleaning device, fan andexhaust stack as shown in figs-Si C- Table £ gives the capture velocities for hoods design under various applications and table gives transport velocities for various types of contaminants, for duct design purposes.

[ \ \ \ \ \ \ i T Y T T T Y T

Fig. 5 Typical industrial exhaust system

4.5 Evaporative cooling: Evaporative coolers or air-washers provide an energy efficient way of providing cold working

conditions in hot and dry climatic conditions. Air is cooled by evaporation of water droplets either sprinkled across the air stream or on wetted porous pads/curtains and in the process the solid contaminants are also removed from the air. An effective evaporative cooling system employs supply system of evaporatively cooled air and almost equal amount of air exhust system. Technically the power exhaust should be controlled so that it increases with the increase in out door air relative humidity.

Indirect evaporative cooling has been effectively used to precool the air entering in the refrigeration coils of an air-conditioning system, thereby reducing the size of refrigeration plants as well as energy and operating costs.

Bibliography: 1. ASHRAE Hand Book. 1992 HVAC Systems and Equipment volume 2 -do- ] 993 Fundamentals volume 3 -do- 1995 HVAC Applications volume

Table - 6 Range of Hood Capture Velocities

Condition of contaminant dispersion

Examples Capture velocity

m/s

Released with no

Evaporation from tanks,degreasing,

velocity into plating etc. still air

0.25 to 0.5

Released at Container filling, low vel. into slow speed moderate conveyor transfer, still air welding

0.5 to 1.0

Active generation into rapid air motion

Barrel filling, chute loading of con v-eyors,crushing cold shakeout

1.0 to 2.5

Released at Grinding, abrasive high vel. blasting, tumbling, 2.5 to 10 into very hot shakeout rapid air

Typical inflow velocity for hoods is 0.5 m/s for calculating the hood area.

A Enclosing \>od 3tn

\ Hooper /

ENCLOSING HOOD

But

\ Hopper 1

NONENCLOSING HOOD

Fig .&a-Enclos ing and Nonenclos ing Hoods

Fig. 6 b Nonenc los ing Hoods

cai .aus! DOWNDRAFT

UPDRAFT COAXIAL

exhaust

plume

source SIDEDRA FT

exhaust convective plume